Before decking the halls with boxwood, be aware of this disease

Even healthy-looking boxwood greenery can harbor a fungal disease that threatens boxwood plants in the garden.
John McDonnell/The Washington Post

Adrian Higgins --- Washington Post

December 14, 2018 2:47 pm

WASHINGTON — Deep green, glossy-leaved, and finely textured, boxwood makes for a perfect holiday wreath. Some folks are put off by its musky smell — I’ve come to like it — but with moderate care, boxwood greenery is slow to dry out and works as a long-lasting matrix for all the little adornments that spruce up and personalize a wreath.

But decorations made from boxwood are not as simple or unburdened as they used to be. The arrival on the East Coast of a fungal disease named boxwood blight means that even healthy-looking wreaths, or greenery for homemade versions, may harbor an organism that will come back to bite your garden boxwood in the spring.

There are ways to minimize the risk, and holiday greenery isn’t the only way the disease spreads, but if you or your immediate neighbors have large, irreplaceable plantings of old boxwood, particularly the classic slow-growing, fine-textured English box, you may want to forgo this wreath material in favor of some other evergreen.

Once the disease manifests itself in a part of the shrub, the whole plant is pretty much doomed. You can spray a healthy shrub preventively — every week or so in the spring and fall — but you may decide that you have better things to do with your time and money.

The blight, previously found in Europe, was first detected in the United States in 2011 and has since spread to approximately two dozen states and Washington, D.C. In Virginia, which has a long history of boxwood gardens, the pathogen is found in approximately 40 jurisdictions, with hot spots in Central and Northern Virginia.

The blight is spreading, but its effects are localized because the spores are sticky and are not airborne as with those of other fungi. Still, if your boxwood-centric garden is afflicted, the results can be devastating because boxwood is an architectural plant that helps give a garden its structure and character. In old properties, boxwood is often a living link between generations, and its abrupt loss can be distressing, not to mention costly.

‘‘I have had people crying in my office, and it’s very sad,’’ said Adria Bordas, horticultural extension agent for Fairfax County and a member of Virginia’s boxwood blight task force.

This year’s abnormal amount of rain in the Mid-Atlantic — more than 60 inches and counting — has been a boon to the pathogen. The spores multiply heartily when leaves remain wet for 48 hours or longer.

‘‘This year, it was explosive in certain locations,’’ said Elizabeth Bush, a plant pathologist for Virginia Tech’s cooperative extension service who receives plant samples from across the state. Last year, she tested a then-record 261 samples, with 32 positive for the disease. In 2018, the number was 409 and 182 tested positive.

What’s the best approach to boxwood greenery this year? The safest course is to harvest boxwood from your own disease-free plants, if you have them. Otherwise, when buying greenery or assembled wreaths, inspect the boxwood carefully for any symptoms, namely brown leafspots leading to branch defoliation and black streaks on stems.

Even healthy-looking greenery may harbor the disease, so wreaths and swags should not be placed near landscape boxwood. After the holidays, this material should be double-bagged and trashed. Don’t compost holiday boxwood or put it out on the curb with the Christmas tree — leaves scattered by the wind or leaf blowers may end up in the wider landscape.

If you have high-value boxwood, you may want to avoid new plantings along with the Christmas greenery. The spores are transported from plant to plant — and site to site — on tools, equipment, clothing and shoes, which should be sanitized between locations. I know one boxwood specialist who keeps a separate set of tools for work crews at each client’s garden.

‘‘I would say interview your landscape professionals or even lawn-mowing company,’’ Bordas said. ‘‘Ask what practices they have between one boxwood customer to the next.’’ What would raise a red flag? ‘‘If they have never heard of the disease,’’ she said.

Even if you observe all these safeguards, another source of spore transference is animals — pets, birds, squirrels and deer.

For all its historical tenacity, the English box (Buxus sempervirens Suffruticosa) has always been peevish about less-than-ideal growing conditions. Its fussiness is usually related to poor cultivation. Its frailties have spawned the introduction of easier-to-grow varieties in recent years. The blight is providing a similar impetus, and new cultivars are on the horizon. Among the tolerant varieties are Green Beauty, Winter Gem, and Wintergreen. Fastigiata is an upright variety perfect for small urban gardens. The slow-growing and handsomely textured Buxus harlandii works as an edging box.

Bordas is optimistic that with varieties such as these and their successors, boxwood’s place in the American garden is secure despite the blight woes. ‘‘We are going to find resistant cultivars, and eventually, English box will be used less and less,’’ she said.